Immune responses to the Mycobacterium tuberculosis-specific antigen ESAT-6 signal subclinical infection among contacts of tuberculosis patients

A Perspective on the Success and Failure of BCG

TB continues to be one of the major public health threats. BCG is the only available vaccine against TB and confers significant protection against the childhood disease. However, the protective efficacy of BCG against adult pulmonary TB, which represents a larger burden of disease, is highly variable. It has been suggested that prior exposure to environmental mycobacteria (EMb) mitigates the anti-TB efficacy of BCG by blocking its duplication or masking its immunogenicity. However, its effectiveness against childhood TB and failure of repeated administration to provide additional benefit against pulmonary TB, suggest of some other mechanisms for the variable efficacy of BCG against the pulmonary disease. Importantly, TB is a heterogeneous disease occurring in different forms and having distinct mechanisms of pathogenesis. While inability of the immune system to contain the bacilli is responsible for TB pathogenesis in infants, an aggravated immune response to Mtb has been blamed for the development of adult pulmonary TB. Available data suggest that EMb play a key role in heightening the immune response against Mtb. In this article, differential efficacy of BCG against childhood and adult TB is explained by taking into account the heterogeneity of TB, mechanisms of TB pathogenesis, and the effect of EMb on anti-Mtb immunity. It is believed that a refined understanding of the success and failure of BCG will help in the development of effective anti-TB vaccines.

Stratification by interferon-γ release assay level predicts risk of incident TB

INTRODUCTION

Targeted testing and treatment of latent TB infection (LTBI) are priorities on the global health agenda, but LTBI management remains challenging. We aimed to evaluate the prognostic value of the QuantiFERON TB-Gold (QFT) test for incident TB, focusing on the interferon (IFN)-γ level, when applied in routine practice in a low TB incidence setting.

METHODS

In this large population-based prospective cohort, we linked QFT results in Norway (1 January 2009-30 June 2014) with national registry data (Norwegian Surveillance System for Infectious Diseases, Norwegian Prescription Database, Norwegian Patient Registry and Statistics Norway) to assess the prognostic value of QFT for incident TB. Participants were followed until 30 June 2016. We used restricted cubic splines to model non-linear relationships between IFN-γ levels and TB, and applied these findings to a competing risk model.

RESULTS

The prospective analyses included 50 389 QFT results from 44 875 individuals, of whom 257 developed TB. Overall, 22% (n=9878) of QFT results were positive. TB risk increased with the IFN-γ level until a plateau level, above which further increase was not associated with additional prognostic information. The HRs for TB were 8.8 (95% CI 4.7 to 16.5), 19.2 (95% CI 11.6 to 31.6) and 31.3 (95% CI 19.8 to 49.5) times higher with IFN-γ levels of 0.35 to <1.00, 1.00 to <4.00 and >4.00 IU/mL, respectively, compared with negative tests (<0.35 IU/mL).

CONCLUSIONS

Consistently, QFT demonstrates increased risk of incident TB with rising IFN-γ concentrations, indicating that IFN-γ levels may be used to guide targeted treatment of LTBI.

Is secretion of IFN-gamma in response to Mycobacterium tuberculosis antigens in youngest children sufficient to play a role in TB diagnostics?

OBJECTIVES

To assess whether children ≤5 years of age, produce sufficient amounts of interferon gamma (IFN-ɣ) in response to phytohaemagglutinin (mitogen), and Mycobacterium tuberculosis antigens (TB antigens) in the QuantiFERON-TB Gold in-Tube test (QFT-GIT), (Cellestis Ltd., Australia).

WORKING HYPOTHESIS

Is TB-antigen-induced IFN-ɣ response in children ≤5 years sufficient to consider QFT-GIT a possible tool for TB diagnostics? Study design, patient-subject selection, and methods: We recruited children 0-17 years old suspected of TB infection to this cross-sectional study, in whom QFT-GIT and TST were performed. We analyzed the median IFN-ɣ levels in mitogen and TB antigen tubes in children ≤5 years and >5 years, and the correlation between IFN-ɣ level in both tubes and age.

RESULTS

A total of 153 children were enrolled, age median was 7.8 (IQR:8), 45 (29.4%) aged ≤5 years (median 3.4, IQR:1.7), 108 > 5 years (median 10.55, IQR:5.93). In the mitogen tubes, the median IFN-ɣ level was higher in children >5 years (median 17.87, IQR:2.1 vs 16.77, IQR:7.6), but surprisingly in the TB antigen tubes it was higher in the younger group (median 0.12, IQR:0.21vs 0.06, IQR:0.09, P = 0.04). We proved a positive correlation between IFN-ɣ level and age in mitogen tubes (r = 0.18, P = 0.03) and a negative correlation in TB antigen tubes (r = -0.17, P = 0.04). In latent tuberculosis infection patients, the latter correlation was found to be even stronger (r = -0.39, P = 0.01).

CONCLUSIONS

The youngest children release sufficient amount of IFN-ɣ in response to TB antigens thus QFT-GIT might be a useful tool for TB diagnostics in this age group.

IFNγ-producing CD4+ T lymphocytes: the double-edged swords in tuberculosis

IFNγ-producing CD4+ T cells (IFNγ+CD4+ T cells) are the key orchestrators of protective immunity against Mycobacterium tuberculosis (Mtb). Primarily, these cells act by enabling Mtb-infected macrophages to enforce phagosome-lysosome fusion, produce reactive nitrogen intermediates (RNIs), and activate autophagy pathways. However, TB is a heterogeneous disease and a host of clinical and experimental findings has also implicated IFNγ+CD4+ T cells in TB pathogenesis. High frequency of IFNγ+CD4+ T cells is the most invariable feature of the active disease. Active TB patients mount a heightened IFNγ+CD4+ T cell response to mycobacterial antigens and demonstrate an IFNγ-inducible transcriptomic signature. IFNγ+CD4+ T cells have also been shown to mediate TB-associated immune reconstitution inflammatory syndrome (TB-IRIS) observed in a subset of antiretroviral therapy (ART)-treated HIV- and Mtb-coinfected people. The pathological face of IFNγ+CD4+ T cells during mycobacterial infection is further uncovered by studies in the animal model of TB-IRIS and in Mtb-infected PD-1-/- mice. This manuscript encompasses the evidence supporting the dual role of IFNγ+CD4+ T cells during Mtb infection and sheds light on immune mechanisms involved in protection versus pathogenesis.

Comparison of pro-inflammatory cytokines of non-healing and healing cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) heals spontaneously within several weeks or months, but, in rare cases, CL-active lesions last for many years. In this study, we assessed cell-mediated immunity in non-healing CL through the measurement of three pro-inflammatory cytokines: Interferon-γ (IFN-γ), IL-17a and CXCL-11. For this, 32 patients afflicted with healing or non-healing CL were recruited in this study. Peripheral blood mononuclear cells (PBMCs) of every patient were treated with three antigens: purified protein derivative (PPD), soluble Leishmania antigen (SLA) and phytohaemagglutinin (PHA). Cytokine quantification was performed using enzyme-linked immunosorbent assay (ELISA) method. Results of our study showed that neither cytokine produced in the presence of a PPD stimulator (as an irrelevant antigen) significantly differed between the healing and non-healing groups (P-value ≥0.05 for all of them). However, IFN-γ, CXCL-11 and IL-17a levels produced in the presence of PHA or SLA were significantly higher within the healing than in the non-healing group (P-value <0.01 for all of them). It seems that appropriate levels of IFN-γ, as well as IL-17a and CXCL-11, contribute to the control of Leishmania infection.

Differential positive TSPOT assay responses to ESAT-6 and CFP-10 in health care workers

BACKGROUND

The TSPOT.TB (TSPOT) diagnostic test for latent tuberculosis infection is based on a cell-mediated response to the Mycobacteria tuberculosis antigens, ESAT-6 and/or CFP-10, producing an "interferon-gamma footprint". We investigated the within-sample and within-subject variability of positive TSPOT assays due to the individual assay antigens' reactivity.

METHODS

Positive TSPOT assay frequencies due to ESAT-6 or CFP-10 among health care workers (HCWs) at 6-month intervals for 18 months were compared. Differences in result interpretation (positive or negative) for ESAT-6 and CFP10 and potential prognostic factors were investigated.

RESULTS

There were 576 positive results in 8805 TSPOT assays representing 2418 participants. A significant difference was detected in positive TSPOT results due to a positive response to either ESAT-6, CFP-10 or both antigens at baseline through 12 M (p < 0.001), but not for the 18 M follow-up. Gender, ethnicity, occupation, previous positive tuberculin skin test (TST) and study site were significantly associated with specific antigen positivity.

CONCLUSIONS

Among our HCW samples with positive TSPOT assays, CFP-10 induced a larger proportion of positive TSPOT results than ESAT-6. Potential causes for this finding include: BCG vaccinated subpopulations, certain jobs, history of positive TST, U.S. birth, and study site. A high proportion of single-positive specimens may reflect false-positives results.

Adult pulmonary tuberculosis as a pathological manifestation of hyperactive antimycobacterial immune response

The intricate relationship between tuberculosis (TB) and immune system remains poorly understood. It is generally believed that weakening of the immune response against Mycobacterium tuberculosis leads to reactivation of latent infection into the active pulmonary disease. However, heterogeneous nature of TB and failure of rationally designed vaccines in clinical trials raises serious questions against the simplistic view of TB as an outcome of weakened immunity. In the wake of accumulating human TB data, it is argued here that a hyperactive antimycobacterial immune response is to blame for the pathogenesis of pulmonary TB in immunocompetent adults. Direct and indirect evidence supporting this notion is presented in this article. Revisiting the role of immune system in TB pathogenesis will pave the way for effective anti-TB vaccines.

T-cell antigens of Mycobacterium immunogenum, an etiological agent of occupational hypersensitivity pneumonitis

The T lymphocyte-mediated immune lung disease hypersensitivity pneumonitis (HP) in machinists is poorly understood for disease mechanisms and diagnosis due in part to lack of information on causative T-cell antigens of the etiological agent Mycobacterium immunogenum (MI). Therefore, overall objective of the current study was to identify T-cell reactive antigens of this recently recognized pathogen. In this direction, purified recombinant form of five of the seroreactive proteins (reported in our initial study), including three cell wall-associated (arbitrarily designated as antigens A through C) and two secretory (AgD & AgE), were examined for their potential to activate antigen-presenting cells (APCs) viz. alveolar macrophages and human monocyte-derived dendritic cells (DCs) and for T-cell reactivity. All five proteins strongly activated APCs by inducing inflammatory cytokines (TNF-α, IL-6 & IL-1α) and nitric oxide (NO), albeit to a varying extent (AgE≥AgD>AgB≥AgA≥AgC), implying their differential potential for activation of APCs. However, only two of the five proteins (AgA, AgD) showed significant T-cell response (T lymphocyte proliferation and IFN-γ secretion) when tested using sensitized T-cells from MI-induced HP mouse model. These antigens also activated the human naïve CD4(+) T cells in presence of autologous DCs as measured using ELISPOT for IFN-γ. Immuno-informatic analysis predicted that the identified T-cell antigens (AgA and AgD) bind more number of class I and class II HLA alleles as compared with the reference immuno-dominant antigens ESAT-6 and CFP-10 from the tuberculous mycobacterial species M. tuberculosis. Predicted human population coverage for the epitopes of AgA (90.87%) and AgD (88.09%) was also higher as compared to those for the reference antigens ESAT-6 (82.42%) and CFP-10 (80.21%). These two antigens were further predicted to be highly immunogenic for class I peptide MHC (pMHC) complex as compared to the reference antigens. Collectively, our results imply that AgA and AgD are T-cell antigens with a high HLA binding frequency as well as population coverage for HLA alleles. This first report on T-cell antigens and epitopes of M. immunogenum is significant as it is expected to open up avenues for understanding pathogenesis mechanisms and developing T-cell-based immunodiagnostic tools for this poorly investigated occupational lung disease.

Prognostic value of interferon-γ release assays, a population-based study from a TB low-incidence country

BACKGROUND

The ability of interferon-γ release assays to predict the development of TB has been investigated in many studies, but few cases develop TB during follow-up limiting the generalisation of results.

METHODS

We assessed QuantiFERON-TB Gold In-Tube test (QFT) results from 15 980 Danish individuals and data on all TB cases in Denmark from 2005 to 2012 and determined the predictive value of the QFT for coprevalent TB (0-90 days after testing) and incident TB (>90 days).

RESULTS

Coprevalent TB was diagnosed in 10.7% (183/1703) and 0.3% (38/13 463) cases with a positive and negative QFT, respectively. For the QFT-positive cases, coprevalent TB was more frequent among persons <35 years compared with those >35  years (19.3% vs 7.2%, p<0.001). The cohort was followed-up for 52 807 person-years, median follow-up time was 3.36 years. For incident TB, the positive and negative predictive values (PPV and NPV) were 1.32% and 99.85%, respectively. Incidence rates (IR) for incident TB among QFT-positives and QFT-negatives were 383 per 10(5) and 45 per 10(5) person-years, respectively. Among cases with a positive QFT, IR for incident TB was associated with time interval since QFT (<2 years, p<0.001), but not with age (<35 years, p=0.087).

CONCLUSIONS

We confirmed a high NPV of the QFT and found positive QFT associated with a higher risk of subsequent incident TB. Overall, the PPV for incident cases was 1.32%, and development of incident TB was associated with time interval after the QFT, but not with age.

Two-Year Follow-up Study of Mycobacterium tuberculosis Antigen-Driven IFN-γ Responses and Macrophage sCD14 Levels After Tuberculosis Contact

Clinical data regarding the prediction of active tuberculosis (TB) development in close TB contacts are scarce. To address this problem, we performed a 2-year follow-up study of Mycobacterium tuberculosis (M.tb) antigen-driven IFN-gamma responses and serum levels of soluble macrophage CD14 receptor in individuals with recent or prolonged M.tb exposure. Between June 2011 and June 2013, we studied 60 healthy Polish adults with recent household or long-term work TB contact and individuals without known M.tb exposure. All of them underwent baseline and repeated testing with IGRA (IFN-gamma release assay) and serum sCD14 ELISA quantification. Frequencies of IGRA results differed at the baseline and follow-up testing. IGRA reversions were noticed in almost one-third of Work TB Contacts and no participants from the Household TB Contact group. IGRA conversions were found in 40 % of Household TB Contacts. No correlation between the IGRA result and the sCD14 level was observed. IFN-γ variability has important implications for clinical practice and requires caution in interpreting the results to distinguish new infections from nonspecific inter-individual variations in cytokine responses. The impairment of IFN-γ response in some individuals with prolonged M.tb exposure representing a resistant immune status does not allow considering IGRA results as reliable and credible. Monitoring the serum sCD14 level can reduce the likelihood of a false prediction of active TB development in close TB contacts showing an M.tb-specific increase in the IFN-gamma production in repeated IGRA testing.

Predicting the Development of Tuberculosis with the Tuberculin Skin Test and QuantiFERON Testing

RATIONALE

The identification of patients with latent tuberculosis infection, who are at higher risk to develop active disease, is an important component of disease control.

OBJECTIVES

We aim to compare the usefulness of the QuantiFERON-TB Gold in-tube assay and the tuberculin skin test to predict the development of active tuberculosis during follow-up, using positive and negative predictive values, positive likelihood ratios, and stratified level of risk.

METHODS

The study included contacts of tuberculosis cases diagnosed between 2007 and 2009. All contacts included were from the first circle of exposure. Tuberculin skin test and QuantiFERON test were performed and a chest radiograph was obtained during the contact's study.

MEASUREMENTS AND MAIN RESULTS

A total of 1,335 contacts were followed up for 4 years: a smear-positive index case was identified for 937 contacts, of whom 15 developed active tuberculosis and had initially presented with positive tuberculin skin test/QuantiFERON results, a normal chest radiograph, and no symptoms. The positive predictive value was 4% for QuantiFERON and 2% for the tuberculin skin test (when ≥5 mm). The probability of developing active disease was 2.36 times higher with a positive QuantiFERON, and 1.3 times higher with a positive tuberculin skin test. The positive predictive value was 17%, and the positive likelihood ratio was 7.53 for untreated contacts with a positive QuantiFERON. Stratifying according to initial QuantiFERON results showed a 6.36 times higher risk of developing active tuberculosis for patients with a QuantiFERON result greater than or equal to 10 IU/ml. Among bacillus Calmette-Guérin-vaccinated patients, a tuberculin skin test induration greater than or equal to 15 mm correlated better with a positive QuantiFERON.

CONCLUSIONS

QuantiFERON results were more accurate than tuberculin skin test results in predicting tuberculosis. Although all contacts with QuantiFERON-positive results are at risk of developing tuberculosis, those with a tuberculin skin test induration greater than or equal to 15 mm and QuantiFERON greater than or equal to 10 IU/ml are at highest risk. This has important implications in the clinical management of tuberculosis contacts.

Tuberculosis vaccines: barriers and prospects on the quest for a transformative tool

The road to a more efficacious vaccine that could be a truly transformative tool for decreasing tuberculosis morbidity and mortality, along with Mycobacterium tuberculosis transmission, is quite daunting. Despite this, there are reasons for optimism. Abetted by better conceptual clarity, clear acknowledgment of the degree of our current immunobiological ignorance, the availability of powerful new tools for dissecting the immunopathogenesis of human tuberculosis, the generation of more creative diversity in tuberculosis vaccine concepts, the development of better fit-for-purpose animal models, and the potential of more pragmatic approaches to the clinical testing of vaccine candidates, the field has promise for delivering novel tools for dealing with this worldwide scourge of poverty.

Multicenter clinical evaluation of three commercial reagent kits based on the interferon-gamma release assay for the rapid diagnosis of tuberculosis in China

OBJECTIVE

To evaluate the performance of three interferon-gamma release assay (IGRA) kits in detecting Mycobacterium tuberculosis infection in China.

METHODS

A multicenter clinical trial was used to compare the effectiveness and application of the three kits. A total of 1026 participants were enrolled at three hospitals, including 597 tuberculosis (TB) patients diagnosed clinically (517 patients with pulmonary TB and 80 patients with extrapulmonary TB) and 429 negative controls (244 patients with pulmonary disease but not TB, or with non-tuberculosis mycobacterial lung diseases, and 185 healthy people). Detection performance indicators including sensitivity, specificity, and the Youden index (YI) were used to evaluate performance.

RESULTS

Through bacterial culture evaluation, 224 of the 517 pulmonary TB patients were positive and all 429 negative controls were negative. When the gold standard bacterial methods were used, the sensitivity, specificity, and YI were 89.7% (201/224), 91.1% (391/429), and 0.81 for T-SPOT.TB, 86.2% (193/224), 87.2% (374/429), and 0.73 for QB-SPOT, and 83.9% (188/224), 88.6% (380/429), and 0.73 for TB-IGRA, respectively. There were no significant differences in the sensitivity and specificity of the three kits.

CONCLUSIONS

The results showed that the three kits had very high sensitivity and specificity and exhibited a good performance for the detection of M. tuberculosis infection.

A Subgroup of Latently Mycobacterium tuberculosis Infected Individuals Is Characterized by Consistently Elevated IgA Responses to Several Mycobacterial Antigens

Elevated antibody responses to Mycobacterium tuberculosis antigens in individuals with latent infection (LTBI) have previously been linked to an increased risk for progression to active disease. Studies in the field focussed mainly on IgG antibodies. In the present study, IgA and/or IgG responses to the mycobacterial protein antigens AlaDH, NarL, 19 kDa, PstS3, and MPT83 were determined in a blinded fashion in sera from 53 LTBI controls, 14 healthy controls, and 42 active TB subjects. Among controls, we found that elevated IgA levels against all investigated antigens were not randomly distributed but concentrated on a subgroup of <30%—with particular high levels in a small subgroup of ~5% comprising one progressor to active TB. Based on a specificity of 100%, anti-NarL IgA antibodies achieved with 78.6% sensitivity the highest accuracy for the detection of active TB compared to healthy controls. In conclusion, the consistently elevated IgA levels in a subgroup of controls suggest higher mycobacterial load, a risk factor for progression to active TB, and together with high IgG levels may have prognostic potential and should be investigated in future large scale studies. The novel antigen NarL may also be promising for the antibody-based diagnosis of active TB cases.

Association of quantitative interferon-γ responses with the progression of naturally acquired Mycobacterium bovis infection in wild European badgers (Meles meles)

Bovine tuberculosis is one of the biggest challenges facing cattle farming in Great Britain. European badgers (Meles meles) are a reservoir host for the causal agent, Mycobacterium bovis. There have been significant recent advances in diagnostic testing for tuberculosis in humans, cattle and badgers, with the development of species-specific assays for interferon-γ (IFN-γ), an important cytokine in tuberculous infections. Using data collected from longitudinal studies of naturally infected wild badgers, we report that the magnitude of the IFN-γ response to M. bovis antigens at the disclosing test event was positively correlated with subsequent progression of disease to a seropositive or excreting state. In addition, we show that the magnitude of the IFN-γ response, despite fluctuation, declined with time after the disclosing event for all badgers, but remained significantly higher in those animals with evidence of disease progression. We discuss how our findings may be related to the immunopathogenesis of natural M. bovis infection in badgers.

Interferon-gamma assay in combination with tuberculin skin test are insufficient for the diagnosis of culture-negative pulmonary tuberculosis

Objective

Early diagnosis of infectious cases and treatment of tuberculosis (TB) are important strategies for reducing the incidence of this disease. Unfortunately, traditional TB diagnostic methods are time-consuming and often unreliable. This study compared the accuracy and reliability of the tuberculin skin test (TST) and interferon (IFN)-γ-based assay (IGRA) for the diagnosis of active pulmonary TB Polish cases that could or could not be confirmed by M. tuberculosis (M.tb) culture.

Methods

In total, 126 adult patients with clinically active TB or non-mycobacterial, community-acquired lung diseases (NMLD) hospitalised at the Regional Specialised Hospital of Tuberculosis, Lung Diseases and Rehabilitation in Tuszyn, Poland were enrolled in the present study. Sensitivity, specificity, positive predicted value (PPV), negative predicted value (NPV), and analytic accuracy (Acc) of TST and IGRA testing for the diagnosis of culture-positive and culture-negative TB patients were calculated. The quantities of IFN-γ produced in the response to M.tb specific antigens (TB Ag – Nil) in the cultures of blood from patients with active TB and NMLD patients were also analysed.

Results

The IGRA sensitivity in culture-positive and culture-negative TB patients was similar, measuring 65.1% and 55.6%, respectively. The sensitivity of TST did not differ from the parameters designated for IGRA, measuring 55.8% in culture-positive and 64.9% in culture-negative TB. The sensitivity of TST and IGRA was age-dependent and decreased significantly with the age of the patients. No differences in the frequency or intensity of M.tb-stimulated IFN-γ production, as assessed by IGRA testing between culture-positive and culture-negative TB were noticed. Significantly lower concentrations of IFN-γ were observed in patients with advanced TB forms compared with those with mild or moderate TB pathologies.

Conclusions

Our results do not show that a combination of IGRA and TST might be a step forward in the diagnosis of culture-negative TB cases. However, M. tuberculosis-stimulated IFN-γ levels might help to assess the extent of pulmonary TB lesions.

The frequencies of IFNγ+IL2+TNFα+ PPD-specific CD4+CD45RO+ T-cells correlate with the magnitude of the QuantiFERON® gold in-tube response in a prospective study of healthy indian adolescents

BACKGROUND

QuantiFERON-TB Gold In-Tube (QFT) is an IFNγ-release assay used in the diagnosis of Mycobacterium tuberculosis (MTB) infection. The risk of TB progression increases with the magnitude of the MTB-specific IFNγ-response. QFT reversion, also associated with low Tuberculin Skin Test responses, may therefore represent a transient immune response with control of M. tuberculosis infection. However, studies at the single cell level have suggested that the quality (polyfunctionality) of the T-cell response is more important than the quantity of cytokines produced.

OBJECTIVE

To explore the quality and/or magnitude of mycobacteria-specific T-cell responses associated with QFT reversion and persistent QFT-positivity.

METHODS

Multi-color flowcytometry on prospectively collected peripheral blood mononuclear cells was applied to assess mycobacteria-specific T-cell responses in 42 QFT positive Indian adolescents of whom 21 became QFT negative (reverters) within one year. Ten QFT consistent negatives were also included as controls.

RESULTS

There was no difference in the qualitative PPD-specific CD4+ T-cell response between QFT consistent positives and reverters. However, compared with QFT consistent positives, reverters displayed lower absolute frequencies of polyfunctional (IFNγ+IL2+TNFα+) CD4+ T-cells at baseline, which were further reduced to the point where they were not different to QFT negative controls one year later. Moreover, absolute frequencies of these cells correlated well with the magnitude of the QFT-response.

CONCLUSION

Whereas specific polyfunctional CD4+ T-cells have been suggested to protect against TB progression, our data do not support that higher relative or absolute frequencies of PPD-specific polyfunctional CD4+ T-cells in peripheral blood can explain the reduced risk of TB progression observed in QFT reverters. On the contrary, absolute frequencies of these cells correlated with the QFT-response, suggesting that this readout reflects antigenic load.

Gamma interferon release assays for detection of Mycobacterium tuberculosis infection

Identification and treatment of latent tuberculosis infection (LTBI) can substantially reduce the risk of developing active disease. However, there is no diagnostic gold standard for LTBI. Two tests are available for identification of LTBI: the tuberculin skin test (TST) and the gamma interferon (IFN-γ) release assay (IGRA). Evidence suggests that both TST and IGRA are acceptable but imperfect tests. They represent indirect markers of Mycobacterium tuberculosis exposure and indicate a cellular immune response to M. tuberculosis. Neither test can accurately differentiate between LTBI and active TB, distinguish reactivation from reinfection, or resolve the various stages within the spectrum of M. tuberculosis infection. Both TST and IGRA have reduced sensitivity in immunocompromised patients and have low predictive value for progression to active TB. To maximize the positive predictive value of existing tests, LTBI screening should be reserved for those who are at sufficiently high risk of progressing to disease. Such high-risk individuals may be identifiable by using multivariable risk prediction models that incorporate test results with risk factors and using serial testing to resolve underlying phenotypes. In the longer term, basic research is necessary to identify highly predictive biomarkers.

Detection of latent tuberculosis infection among laboratory personnel at a University Hospital in Eastern Saudi Arabia using an interferon gamma release assay

BACKGROUND/AIMS

A few recent reports have demonstrated an elevated prevalence of latent tuberculosis infection (LTBI) among laboratory personnel. We sought to evaluate the prevalence of LTBI among laboratory personnel using the QuantiFERON-TB Gold In-Tube (QFT-GIT) assay and to assess the risk factors associated with positive test results.

METHODS

The study population included laboratory personnel who were working in the routine diagnostic laboratories of different departments of a university hospital. Subjects were interviewed using a standardized questionnaire that assessed information related to risk factors for LTBI and underwent the QFT-GIT assay.

RESULTS

Positive QFT-GIT tests results were detected in 19.4% (26/134) of the laboratory personnel. The following factors were significantly associated with positive QFT-GIT results: age≥30 years [odds ratio (OR): 4.741, 95% CI: 1.41-17.50, P=0.004]; duration of employment in the healthcare profession >10 years (P<0.0001); and non-Saudi nationality (OR: 21.67, 95% CI: 6.69-73.94, P<0.0001).

CONCLUSION

These data highlight the need for effective institutional TB infection control plans. Additionally, our data reinforce the necessities of pre-employment and regular LTBI screening of laboratory personnel and the importance of offering preventive therapies to positive subjects to prevent the progression to active disease.

Relevance of bovine tuberculosis research to the understanding of human disease: historical perspectives, approaches, and immunologic mechanisms

Pioneer studies on infectious disease and immunology by Jenner, Pasteur, Koch, Von Behring, Nocard, Roux, and Ehrlich forged a path for the dual-purpose with dual benefit approach, demonstrating a profound relevance of veterinary studies for biomedical applications. Tuberculosis (TB), primarily due to Mycobacterium tuberculosis in humans and Mycobacterium bovis in cattle, is an exemplary model for the demonstration of this concept. Early studies with cattle were instrumental in the development of the use of Koch's tuberculin as an in vivo measure of cell-mediated immunity for diagnostic purposes. Calmette and Guerin demonstrated the efficacy of an attenuated M. bovis strain (BCG) in cattle prior to use of this vaccine in humans. The interferon-γ release assay, now widely used for TB diagnosis in humans, was developed circa 1990 for use in the Australian bovine TB eradication program. More recently, M. bovis infection and vaccine efficacy studies with cattle have demonstrated a correlation of vaccine-elicited T cell central memory (TCM) responses to vaccine efficacy, correlation of specific antibody to mycobacterial burden and lesion severity, and detection of antigen-specific IL-17 responses to vaccination and infection. Additionally, positive prognostic indicators of bovine TB vaccine efficacy (i.e., responses measured after infection) include: reduced antigen-specific IFN-γ, iNOS, IL-4, and MIP1-α responses; reduced antigen-specific expansion of CD4(+) T cells; and a diminished activation profile on T cells within antigen stimulated cultures. Delayed type hypersensitivity and IFN-γ responses correlate with infection but do not necessarily correlate with lesion severity whereas antibody responses generally correlate with lesion severity. Recently, serologic tests have emerged for the detection of tuberculous animals, particularly elephants, captive cervids, and camelids. B cell aggregates are consistently detected within tuberculous lesions of humans, cattle, mice and various other species, suggesting a role for B cells in the immunopathogenesis of TB. Comparative immunology studies including partnerships of researchers with veterinary and medical perspectives will continue to provide mutual benefit to TB research in both man and animals.

Combination of cytokine responses indicative of latent TB and active TB in Malawian adults

Background

An IFN-γ response to M. tuberculosis-specific antigens is an effective biomarker for M. tuberculosis infection but it cannot discriminate between latent TB infection and active TB disease. Combining a number of cytokine/chemokine responses to M. tuberculosis antigens may enable differentiation of latent TB from active disease.

Methods

Asymptomatic recently-exposed individuals (spouses of TB patients) were recruited and tuberculin skin tested, bled and followed-up for two years. Culture supernatants, from a six-day culture of diluted whole blood samples stimulated with M. tuberculosis-derived PPD or ESAT-6, were measured for IFN-γ, IL-10, IL-13, IL-17, TNF-α and CXCL10 using cytokine ELISAs. In addition, 15 patients with sputum smear-positive pulmonary TB were recruited and tested.

Results

Spouses with positive IFN-γ responses to M. tuberculosis ESAT-6 (>62.5 pg/mL) and TB patients showed high production of IL-17, CXCL10 and TNF-α. Higher production of IL-10 and IL-17 in response to ESAT-6 was observed in the spouses compared with TB patients while the ratios of IFN-γ/IL-10 and IFN-γ/IL-17 in response to M. tuberculosis-derived PPD were significantly higher in TB patients compared with the spouses. Tuberculin skin test results did not correlate with cytokine responses.

Conclusions

CXCL10 and TNF-α may be used as adjunct markers alongside an IFN-γ release assay to diagnose M. tuberculosis infection, and IL-17 and IL-10 production may differentiate individuals with LTBI from active TB.

Interferon Gamma Response to Combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10, Each Related to a Single Recombinant Protein ofMycobacterium tuberculosisin Individuals from Tuberculosis Endemic Areas

Several antigens of Mycobacterium tuberculosis have been identified and specificity to one or multiple antigens could determine the distinction between protective and pathogenic host reaction. Therefore T cell immune response to combinations 38 kDa/CFP-10, 38 kDa/MPT-64, ESAT-6/MPT-64 and ESAT-6/CFP-10 (each related to a single protein of Mycobacterium tuberculosis) in individuals from tuberculosis endemic areas have been examined. ELISA was used to detect IFN-gamma production in PBMC priming with single proteins and combinations in a panel of 105 individuals: 38 tuberculosis patients (6 untreated and 32 treated) and 67 healthy controls with tuberculin skin test positive or negative (TST). Brazilian TB patients highly recognized ESAT-6 (66%), but combinations improved response in the following order: ESAT-6/MPT-64 (89%) > ESAT-6/CFP-10 (73%) > 38 kDa/CFP-10 (70%), the last combination showing the highest specificity (TST(/) = 42% and TST(-) = 83%). Average IFN-gamma production in TB patients was signifi-cantly higher for 38 kDa/CFP-10 (P = 0.012) and 38 kDa/MPT-64 (P <0.035), when compared to single antigens. None of the combinations was able to discriminate TB patients from TST(+) controls; however, 38 kDa/CFP-10 displayed a borderline significance (P = 0.053). Similar to the ESAT-6/CFP-10 combination, IFN-gamma response to 38 kDa/CFP-10 showed an increased tendency in treated patients, although not signifi-cant (P = 0.16). We demonstrated for the first time that 38 kDa/CFP-10 had prediction sensitivity for TB patients similar to the ESAT-6/CFP-10 combination and also significant response improvement related to the single proteins with more selective reactivity among TST-positive individuals, which could be of potential interest for diagnostic evaluation for tuberculosis infection.

Heparin-binding haemagglutinin, a new tool for the detection of latent Mycobacterium tuberculosis infection in hemodialysis patients

Background

Patients with end-stage renal disease (ESRD) and latently infected with Mycobacterium tuberculosis (LTBI) are at higher risk to develop tuberculosis (TB) than healthy subjects. Interferon-gamma release assays (IGRAs) were reported to be more sensitive than tuberculin skin tests for the detection of infected individuals in dialysis patients.

Methods

On 143 dialysis patients prospectively enrolled, we compared the results from the QuantiFERON®-TB Gold assay (QFT), to those of an IGRA in response to in vitro stimulation of circulating mononuclear cells with the mycobacterial latency antigen Heparin-Binding Haemagglutinin purified from Mycobacterium bovis BCG (native HBHA, nHBHA).

Results

Seven patients had a past history of active TB and 1 had an undetermined result with both IGRAs. Among the other 135 patients, 94 had concordant results with the QFT and nHBHA-IGRA, 40.0% being negative and therefore not latently infected, and 29.6% being positive and thus LTBI. Discrepant results between these tests were found for 36 patients positive only with the nHBHA-IGRA and 5 only with the QFT.

Conclusions

The nHBHA-IGRA is more sensitive than the QFT for the detection of LTBI dialysis patients, and follow-up of the patients will allow us to define the clinical significance of discrepant results between the nHBHA-IGRA and the QFT.

Mycobacterium tuberculosis PPE protein Rv0256c induces strong B cell response in tuberculosis patients

Tuberculosis (TB) is one of the most important diseases of humans and major public health problem worldwide. Early and accurate diagnosis of TB is necessary for the treatment, prevention, and control of TB. Therefore, it is important to identify suitable antigens that can differentiate active tuberculosis patients from BCG-vaccinated individuals. In the present study, we have used Rv0256c (PPE2) protein of Mycobacterium tuberculosis to screen the sera of infected patients belonging to different clinical TB presentations, and BCG-vaccinated clinically healthy individuals by enzyme immunoassay. Our results demonstrated that Rv0256c displayed stronger and specific immunoreactivity against the sera obtained from clinically active tuberculosis patients compared to PPD and ESAT-6 and could differentiate the TB-patients from the BCG-vaccinated controls. Importantly, Rv0256c was also found to detect even the extrapulmonary and smear-negative pulmonary cases which often are tedious and difficult to detect using conventional diagnostic methods. This study suggests that Rv0256c can be used as a potential marker for the serodiagnosis of tuberculosis patients.

Prevalência de infecção latente pelo Mycobacterium tuberculosis entre estudantes da área da saúde de uma universidade pública em Vitória, ES, Brasil

Este artigo tem por objetivo determinar a prevalência da infecção pelo Mycobacterium tuberculosis em acadêmicos de enfermagem e medicina da Universidade Federal do Espírito Santo. Estudo de corte transversal no qual os dados foram coletados através de questionário, composto de questões abertas e fechadas sobre características pessoais; informações a respeito da tuberculose; utilização de medidas preventivas, etc. Aplicou-se teste tuberculínico, com leitura após 72h por enfermeiros treinados, considerando como ponte de corte positivo 10 mm de enduração. Participaram 225 voluntários, sendo 98 estudantes da Medicina e 127 da Enfermagem. A positividade ao teste tuberculínico fora encontrada em 54 estudantes de ambos os cursos, resultando uma prevalência de 24%. Entre os Estudantes de Enfermagem o resultado do TST positivo foi obtido em 24% e nos Estudantes de Medicina em 23%, sendo esta diferença não significativa estatisticamente. Faz-se necessário um programa de realização de teste tuberculínico, de rotina, para confirmação de viragem tuberculínica, combinado com intervenções para reduzir o risco de transmissão nosocomial no local da prática, bem como a realização de outros estudos para avaliar a eficácia de novos testes para detecção de tuberculose latente.

Biomarkers of latent TB infection

For the last 100 years, the tuberculin skin test (TST) has been the only diagnostic tool available for latent TB infection (LTBI) and no biomarker per se is available to diagnose the presence of LTBI. With the introduction of M. tuberculosis-specific IFN-gamma release assays (IGRAs), a new area of in vitro immunodiagnostic tests for LTBI based on biomarker readout has become a reality. In this review, we discuss existing evidence on the clinical usefulness of IGRAs and the indefinite number of potential new biomarkers that can be used to improve diagnosis of latent TB infection. We also present early data suggesting that the monocyte-derived chemokine inducible protein-10 may be useful as a novel biomarker for the immunodiagnosis of latent TB infection.

Rapid identification and drug susceptibility screening of ESAT-6 secreting Mycobacteria by a NanoELIwell assay

To meet the global needs of tuberculosis (TB) control, a nanoELIwell device was developed as a multifunctional assay for TB diagnosis and drug susceptibility testing. The device integrates on-chip culturing of mycobacteria, immunoassay, and high-resolution fluorescent imaging. Mycobacterium smegmatis and Mycobacterium kansasii were used as models of Mycobacterium tuberculosis to evaluate device integrity by using antigens, Ag85 and ESAT-6, as biomarkers. As a result, the nanoELIwell device detected antigens released from a single bacterium within 24–48-hour culture. Antimycobacterial drug-treated M. smegmatis showed significant decreased in Ag85 antigen production when treated with ethambutol and no change in antigen production when treated with rifampin, demonstrating drug susceptibility and resistance, respectively. The nanoELIwell assay also distinguished the ESAT-6-secreting M. kansasii from the non-ESAT-6-secreting M. simiae. The combination of microwell technology and ELISA assay holds potential to the development of a rapid, sensitive, and specific diagnostics and susceptibility testing of TB.

Risk stratification of latent tuberculosis defined by combined interferon gamma release assays

BACKGROUND

Most individuals infected with Mycobacterium tuberculosis develop latent tuberculosis infection (LTBI). Some may progress to active disease and would benefit from preventive treatment yet no means currently exists to predict who will reactivate. Here, we provide an approach to stratify LTBI based on IFN-γ responses to two antigens, the recombinant Early-Secreted Antigen Target-6 (rESAT-6) and the latency antigen Heparin-Binding Haemagglutinin (HBHA).

METHODS

We retrospectively analyzed results from in-house IFN-γ-release assays with HBHA (HBHA-IGRA) and rESAT-6 (rESAT-6-IGRA) performed during a 12-year period on serial blood samples (3 to 9) collected from 23 LTBI subjects in a low-TB incidence country. Both the kinetics of the absolute IFN-γ concentrations secreted in response to each antigen and the dynamics of HBHA/rESAT-6-induced IFN-γ concentrations ratios were examined.

RESULTS

This analysis allowed the identification among the LTBI subjects of three major groups. Group A featured stable HBHA and rESAT-6-IGRA profiles with an HBHA/rESAT-6 ratio persistently higher than 1, and with high HBHA- and usually negative rESAT-6-IGRA responses throughout the study. Group B had changing HBHA/rESAT-6 ratios fluctuating from 0.0001 to 10,000, with both HBHA and rESAT-6 responses varying over time at least once during the follow-up. Group C was characterized by a progressive disappearance of all responses.

CONCLUSIONS

By combining the measures of IFN-γ concentrations secreted in response to an early and a latency antigens, LTBI subjects can be stratified into different risk groups. We propose that disappearing responses indicate cure, that persistent responses to HBHA with HBHA/rESAT-6 ratios ≥ 1 represent stable LTBI subjects, whereas subjects with ratios varying from >1 to <1 should be closely monitored as they may represent the highest-risk group, as illustrated by a case report, and should therefore be prioritized for preventive treatment.

Helminths and skewed cytokine profiles increase tuberculin skin test positivity in Warao Amerindians

The immune regulatory mechanisms involved in the acquisition of Mycobacterium tuberculosis infection in children are largely unknown. We investigated the influence of parasitic infections, malnutrition and plasma cytokine profiles on tuberculin skin test (TST) positivity in Warao Amerindians in Venezuela. Pediatric household contacts of sputum smear-positive tuberculosis (TB) cases were enrolled for TST, chest radiograph, plasma cytokine analyses, QuantiFERON-TB Gold In-Tube (QFT-GIT) testing and stool examinations. Factors associated with TST positivity were studied using generalized estimation equations logistic regression models. Of the 141 asymptomatic contacts, 39% was TST-positive. After adjusting for age, gender and nutritional status, TST positivity was associated with Trichuris trichiura infections (OR 3.5, 95% CI 1.1-11.6) and low circulating levels of T helper 1 (Th1) cytokines (OR 0.51, 95% CI 0.33-0.79). Ascaris lumbricoides infections in interaction with Th2- and interleukin (IL)-10-dominated cytokine profiles were positively associated with TST positivity (OR 3.1, 95% CI 1.1-8.9 and OR 2.4, 95% CI 1.04-5.7, respectively). A negative correlation of QFT-GIT mitogen responses with Th1 and Th2 levels and a positive correlation with age were observed (all p < 0.01). We conclude that helminth infections and low Th1 cytokine plasma levels are significantly associated with TST positivity in indigenous Venezuelan pediatric TB contacts.

A comparative analysis of polyfunctional T cells and secreted cytokines induced by Bacille Calmette-Guérin immunisation in children and adults

BCG vaccine is one of the most commonly-administered vaccines worldwide. Studies suggest the protective efficacy of BCG against TB is better for children than for adults. One potential explanation is that BCG induces a better protective immune response in children. Twenty six children and adults were immunised with BCG. The proportion of Th1-cytokine-producing mycobacterial-specific T cells, and the concentrations of secreted cytokines, were measured before and 10 weeks after BCG immunisation. A significant increase in the proportion of mycobacterial-specific cytokine-producing T cells was observed in both age groups. After BCG immunisation, children and adults had comparable proportions of mycobacterial-specific polyfunctional CD4 T cells when measured relative to the total number of CD4 T cells. However, relative to the subset of Th-1-cytokine-producing CD4 T cells, the proportion of polyfunctional cells was greater in children. Concentrations of secreted cytokines were comparable in children and adults. These findings suggest that the mycobacterial-specific cell-mediated immune response induced by BCG immunisation in children and adults is similar. The implication of a shift to a more polyfunctional immune response within the Th1-cytokine-producing CD4 T cells in children is uncertain as this aspect of the immune response has not been assessed as a potential correlate of protection against TB.

The HyVac4 subunit vaccine efficiently boosts BCG-primed anti-mycobacterial protective immunity

BACKGROUND

The current vaccine against tuberculosis (TB), BCG, has failed to control TB worldwide and the protective efficacy is moreover limited to 10-15 years. A vaccine that could efficiently boost a BCG-induced immune response and thus prolong protective immunity would therefore have a significant impact on the global TB-burden.

METHODS/FINDINGS

In the present study we show that the fusion protein HyVac4 (H4), consisting of the mycobacterial antigens Ag85B and TB10.4, given in the adjuvant IC31® or DDA/MPL effectively boosted and prolonged immunity induced by BCG, leading to improved protection against infection with virulent M. tuberculosis (M.tb). Increased protection correlated with an increased percentage of TB10.4 specific IFNγ/TNFα/IL-2 or TNFα/IL-2 producing CD4 T cells at the site of infection. Moreover, this vaccine strategy did not compromise the use of ESAT-6 as an accurate correlate of disease development/vaccine efficacy. Indeed both CD4 and CD8 ESAT-6 specific T cells showed significant correlation with bacterial levels.

CONCLUSIONS/SIGNIFICANCE

H4-IC31® can efficiently boost BCG-primed immunity leading to an increased protective anti-M.tb immune response dominated by IFNγ/TNFα/IL-2 or TNFα/IL2 producing CD4 T cells. H4 in the CD4 T cell inducing adjuvant IC31® is presently in clinical trials.

Immune markers and correlates of protection for vaccine induced immune responses

Vaccines have been a major innovation in the history of mankind and still have the potential to address the challenges posed by chronic intracellular infections including tuberculosis, HIV and malaria which are leading causes of high morbidity and mortality across the world. Markers of an appropriate humoral response currently remain the best validated correlates of protective immunity after vaccination. Despite advancements in the field of immunology over the past few decades currently there are, however, no sufficiently validated immune correlates of vaccine induced protection against chronic infections in neither human nor veterinary medicine. Technological and conceptual advancements within cell-mediated immunology have led to a number of new immunological read-outs with the potential to emerge as correlates of vaccine induced protection. For T(H)1 type responses, antigen-specific production of interferon-gamma (IFN-γ) has been promoted as a quantitative marker of protective cell-mediated immune responses over the past couple of decades. More recently, however, evidence from several infections has pointed towards the quality of the immune response, measured through increased levels of antigen-specific polyfunctional T cells capable of producing a triad of relevant cytokines, as a better correlate of sustained protective immunity against this type of infections. Also the possibilities to measure antigen-specific cytotoxic T cells (CTL) during infection or in response to vaccination, through recombinant major histocompatibility complex (MHC) class I tetramers loaded with relevant peptides, has opened a new vista to include CTL responses in the evaluation of protective immune responses. Here, we review different immune markers and new candidates for correlates of a protective vaccine induced immune response against chronic infections and how successful they have been in defining the protective immunity in human and veterinary medicine.

Roles and underlying mechanisms of ESAT-6 in the context of Mycobacterium tuberculosis-host interaction from a systems biology perspective

The 6kDa early secreted antigenic target (ESAT-6), an important and intensively studied virulence factor of Mycobacterium tuberculosis, acts alone or in combination with CFP-10 to influence the outcome of the host-pathogen interaction. Secreted ESAT-6 can disturb the activation of macrophages, induce apoptosis and subvert host immunity. ESAT-6 mediated autophagosome formation and TLR signaling deviation lead to abnormal activation of NF-κB and subsequent erroneous expression of NF-κB-dependent genes. The C-terminal amino acid residues 90-95 in ESAT-6 are essential for the interaction with host. In-depth appreciation of the multiple roles of ESAT-6 upon host can inform improvements for novel vaccines and diagnostic tools for tuberculosis.

Correlation of mycobacterium tuberculosis specific and non-specific quantitative Th1 T-cell responses with bacillary load in a high burden setting

Background

Measures of bacillary load in patients with tuberculosis (TB) may be useful for predicting and monitoring response to treatment. The relationship between quantitative T-cell responses and mycobacterial load remains unclear. We hypothesised that, in a HIV-prevalent high burden setting, the magnitude of mycobacterial antigen-specific and non-specific T-cell IFN-γ responses would correlate with (a) bacterial load and (b) culture conversion in patients undergoing treatment.

Methods

We compared baseline (n = 147), 2 (n = 35) and 6 month (n = 13) purified-protein-derivative (PPD) and RD1-specific (TSPOT.TB and QFT-GIT) blood RD1-specific (TSPOT.TB; QFT-GIT) responses with associates of sputum bacillary load in patients with culture-confirmed TB in Cape Town, South Africa.

Results

IFN-γ responses were not associated with liquid culture time-to-positivity, smear-grade, Xpert MTB/RIF-generated cycle threshold values or the presence of cavities on the chest radiograph in patients with culture-confirmed TB and irrespective of HIV-status. 2-month IGRA conversion rates (positive-to-negative) were negligible [<11% for TSPOT.TB (3/28) and QFT-GIT (1/29)] and lower compared to culture [60% (21/35); p<0.01].

Conclusions

In a high burden HIV-prevalent setting T-cell IFN-γ responses to M. tuberculosis-specific and non-specific antigens do not correlate with bacillary load, including Xpert MTB/RIF-generated C_T values, and are therefore poorly suited for monitoring treatment and prognostication.

Redefining latent tuberculosis

TB remains a public health problem worldwide, in part due to latent TB infection that serves as a global reservoir of potential disease. In the 20th century, the natural history of TB was defined by clinical symptoms, the tuberculin skin test and chest x-ray. The last decade witnessed the invention and application of IFN-γ release assays and newer immunological tools that enabled a re-appraisal of the natural history of TB. Here, we review the conventional understanding of latent TB and recount how immunology has redefined latent TB as a spectrum of pathogen burden and host immune control. We discuss recent and future advances in the fields of TB immunology and diagnostics that will improve public health strategies to control TB.

Mycobacteria and biological response modifiers: two sides of the relationship

With increasing use of biological response modifiers (BRMs) for various systemic inflammatory diseases there is a need to be vigilant about complications with the use of these therapies. It is important to have appropriate screening for the infections in patients requiring BRMs. However, many studies have reported benefits of certain BRMs in the treatment of infections such as tuberculosis as adjuncts. Continued research and technical advances in immunogenetics helps understand complex mechanisms in the usage of the BRMs. This article summarizes the different aspects of the relationship between mycobacterial infections and the use of various BRMs for inflammatory conditions.

Predictive value of interferon-γ release assays for incident active tuberculosis: a systematic review and meta-analysis

BACKGROUND

We aimed to assess whether interferon-γ release assays (IGRAs) can predict the development of active tuberculosis and whether the predictive ability of these tests is better than that of the tuberculin skin test (TST).

METHODS

Longitudinal studies of the predictive value for active tuberculosis of in-house or commercial IGRAs were identified through searches of PubMed, Embase, Biosis, and Web of Science and complementary manual searches up to June 30, 2011. Eligible studies included adults or children, with or without HIV, who were free of active tuberculosis at study baseline. We summarised incidence rates in forest plots and pooled data with random-effects models when appropriate. We calculated incidence rate ratios (IRR) for rates of disease progression in IGRA-positive versus IGRA-negative individuals.

FINDINGS

15 studies had a combined sample size of 26 680 participants. Incidence of tuberculosis during a median follow-up of 4 years (IQR 2-6), even in IGRA-positive individuals, was 4-48 cases per 1000 person-years. Seven studies with no possibility of incorporation bias and reporting baseline stratification on the basis of IGRA results showed a moderate association between positive results and subsequent tuberculosis (pooled unadjusted IRR 2·10, 95% CI 1·42-3·08). Compared with test-negative results, IGRA-positive and TST-positive results were much the same with regard to the risk of tuberculosis (pooled IRR in the five studies that used both was 2·11 [95% CI 1·29-3·46] for IGRA vs 1·60 [0·94-2·72] for TST at the 10 mm cutoff). However, the proportion of IGRA-positive individuals in seven of 11 studies that assessed both IGRAs and TST was generally lower than TST-positive individuals.

INTERPRETATION

Neither IGRAs nor the TST have high accuracy for the prediction of active tuberculosis, although use of IGRAs in some populations might reduce the number of people considered for preventive treatment. Until more predictive biomarkers are identified, existing tests for latent tuberculosis infection should be chosen on the basis of relative specificity in different populations, logistics, cost, and patients' preferences rather than on predictive ability alone.

FUNDING

Special Programme for Research and Training in Tropical Diseases (WHO), Wellcome Trust, Canadian Institutes of Health Research, UK Medical Research Council, and the European and Developing Countries Clinical Trials Partnership.

Novel M tuberculosis antigen-specific T-cells are early markers of infection and disease progression

BACKGROUND

Mycobacterium tuberculosis Region-of-Difference-1 gene products present opportunities for specific diagnosis of M. tuberculosis infection, yet immune responses to only two gene-products, Early Secretory Antigenic Target-6 (ESAT-6) and Culture Filtrate Protein-10 (CFP-10), have been comprehensively investigated.

METHODS

T-cell responses to Rv3873, Rv3878 and Rv3879c were quantified by IFN-γ-enzyme-linked-immunospot (ELISpot) in 846 children with recent household tuberculosis exposure and correlated with kinetics of tuberculin skin test (TST) and ESAT-6/CFP-10-ELISpot conversion over six months and clinical outcome over two years.

RESULTS

Responses to Rv3873, Rv3878, and Rv3879c were present in 20-25% of contacts at enrolment. Rv3873 and Rv3879c responses were associated with and preceded TST conversion (P=0.02 and P=0.04 respectively), identifying these antigens as early targets of cell-mediated immunity following M. tuberculosis exposure. Responses to Rv3873 were additionally associated with subsequent ESAT-6/CFP-10-ELISpot conversion (P=0.04). Responses to Rv3873 and Rv3878 predicted progression to active disease (adjusted incidence rate ratio [95% CI] 3.06 [1.05,8.95; P=0.04], and 3.32 [1.14,9.71; P=0.03], respectively). Presence of a BCG-vaccination scar was associated with a 67% (P=0.03) relative risk reduction for progression to active tuberculosis.

CONCLUSIONS

These RD1-derived antigens are early targets of cellular immunity following tuberculosis exposure and T-cells specific for these antigens predict progression to active tuberculosis suggesting diagnostic and prognostic utility.

Diagnosing latent tuberculosis in high-risk individuals: rising to the challenge in high-burden areas

A key challenge to greater progress in tuberculosis (TB) control is the reservoir of latent TB infection (LTBI), which represents a huge long-lived reservoir of potential TB disease. In parts of Africa, as many as 50% of 15-year-olds and 77%-89% of adults have evidence of LTBI. A second key challenge to TB control is the human immunodeficiency virus (HIV)-associated TB epidemic, and Africa alone accounts for one-quarter of the global burden of HIV-associated TB. HIV co-infection promotes both reactivation TB from LTBI and rapidly progressive primary TB following recent exposure to Mycobacterium tuberculosis. Preventing active TB and tackling latent infection in addition to the Directly Observed Treatment, Short-Course (DOTS) strategy could improve TB control in high-burden settings, especially where there is a high prevalence of HIV co-infection. Current strategies include intensified case finding (ICF), TB infection control, antiretroviral therapy (ART), and isoniazid preventive therapy (IPT). Although ART has been widely rolled out, ICF and IPT have not. A key factor limiting the rollout and effectiveness of IPT and ICF is the limitations of existing tools to both diagnose LTBI and identify those persons most at risk of progressing to active TB. In this review, we examine the obstacles and consider current progress toward the development of new tools to address this pressing global problem.

Incipient and subclinical tuberculosis: defining early disease states in the context of host immune response

Latent Mycobacterium tuberculosis infection (LTBI) and active tuberculosis (TB) are 2 ends of a spectrum of states ranging from asymptomatic infection to overt disease. While progressing from LTBI to TB, patients often undergo asymptomatic states with detectable manifestations indicative of disease. Such asymptomatic disease states frequently remain undiagnosed, and their manifestations and duration are mostly dependent on host immune response. Various terms referring to such states are used in the literature, often interchangeably and without explicit definitions. Defining these intermediate states in concrete terms is important for pragmatic reasons, as they might impact upon the diagnostic performance of TB biomarkers and could also present targets for therapeutic interventions. We here propose definitions for 2 commonly used terms, "incipient" and "subclinical" TB, to describe asymptomatic disease states occurring at opposite ends of the host response spectrum. We propose using the term "incipient TB" when referring to early, contained disease in asymptomatic, relatively immunocompetent persons. In contrast, we propose using the term "subclinical TB" to refer to disease in asymptomatic, immunocompromised individuals in whom it is largely associated with loss of effective containment. The rationale for this article is to facilitate the discussion of such early disease states, especially in relation to their impact on TB biomarker discovery and assessment of new diagnostics, and with regard to treatment decisions and ultimately outcome.

Disseminated tuberculosis in human immunodeficiency virus infection: ineffective immunity, polyclonal disease and high mortality

BACKGROUND

Disseminated tuberculosis (TB) is a major cause of death in patients with the acquired immune-deficiency syndrome (AIDS), but its pathogenesis and clinical features have not been defined prospectively.

METHODS

Human immunodeficiency virus (HIV) infected adults with a CD4 count ≥ 200 cells/μl and bacille Calmette-Guérin scar underwent immunologic evaluation and subsequent follow-up.

RESULTS

Among 20 subjects who developed disseminated TB, baseline tuberculin skin tests were ≥15 mm in 14 (70%) and lymphocyte proliferative responses to Mycobacterium tuberculosis were positive in 14 (70%). At the time of diagnosis, fever ≥2 weeks plus ≥5 kg weight loss was reported in 16 (80%) patients, abnormal chest X-rays in 7/17 (41%), and positive sputum cultures in 10 (50%); median CD4 count was 30 cells/μl (range 1-122). By insertion sequence (IS) 6110 analysis, 14 (70%) blood isolates were clustered and 3/8 (37%) concurrent sputum isolates represented a different strain (polyclonal disease). Empiric TB treatment was given to eight (40%) patients; 11 (55%) died within a month.

CONCLUSIONS

Disseminated TB in HIV occurs with cellular immune responses indicating prior mycobacterial infection, and IS6110 analysis suggests an often lethal combination of reactivation and newly acquired infection. Control will require effective prevention of both remotely and recently acquired infection, and wider use of empiric therapy in patients with advanced AIDS and prolonged fever.